In the dental practice, certain synthetic compositions are used for making artificial dental parts, such as crowns, individual teeth, bridges, dentures or parts thereof, which compositions exhibit an undesired tinge of yellow caused by the specific color of polymerisation initators contained therein. Such tinge may be permanently removed in a subsequent bleaching step by an irreversible reaction actuated by radiation to obtain a hue corresponding to the natural tooth color. Typically, radiation in a range from about 400 nm to about 500 nm (with a maximum at about 460 nm) is required for this bleaching process, the irradiation taking place over substantial period of time of for instance 30 min. This irradiation at the same time results in a desired post-polymerisation of the material.
German Offenlegungsschrift No. 29 01 534 discloses an irradiation apparatus for use in the dental field which employs radiation in the UVA spectral range (about 320 nm to about 400 nm) or in the near-UVA visible spectral range, for curing dental fillings made of synthetic material. In order to direct the radiation to the limited area of a tooth filling within the mouth of a patient, the desired spectral portion of the radiation emitted by a lamp is focussed by an ellipsoidal selective reflector onto the input end of an optical wave guide and directed by means of the wave guide onto the location to be irradiated over a period of time of for instance 20 to 30 s. During this relatively short irradiation period, the known apparatus is hand-held by the dentist. The selective reflector of the known apparatus ensures that only the desired radiation enters the optical waveguide while both, dangerous radiation of shorter wavelengths and heat radiation predominantly produced by the lamp, are transmitted through the reflector to the rear side thereof.
The known apparatus is not suited for the present purpose of a bleaching treatment, because it is designed as a hand-held device, because it is made for irradiating very limited areas only, and because of the shortness of the individual periods of operation.
It is an object of the invention to provide an apparatus for irradiating dental objects which permits a uniform irradiation of substantially the entire surface of the objects during a comparatively long period of time and which exploits the desired radiation produced as completely as possible.
Another object of the invention is to provide an apparatus of the above type, which is simple in operation and easy to handle.
As a further object of the invention an apparatus should be provided which irradiates all free surfaces of the respective object without requiring a rotation or other movement of the object during the irradiation procedure.
It is another object of the invention to devise an apparatus for irradiating dental objects with radiation of a desired "cold" spectral range, at the time avoiding any heating of the object as completely as possible. This is of particular importance because excessive temperatures may damage or destroy the synthetic material of the objects. Furthermore, in dental objects containing parts of metal and parts of synthetic material, excessive heat may deteriorate the connection between the different parts due to the difference in their thermal expansion coefficients. In view of this particular problem, it is another object of the invention to devise an apparatus for irradiating dental objects so that the temperature of the object is maintained below about 50.degree. C.
As a further object of the invention, an apparatus for irradiating dental objects is to be provided, which allows an evacuation of the treatment zone. Such evacuation may be required if the respective dental object to the irradiated is made of a polymer which tends to form undesired layers on its surface when exposed to oxygen during the irradiation process.
It is a further object of the invention to provide an apparatus for irradiating dental objects, which apparatus allows easy access to the treatment zone for inserting and removing the respective dental objects, as well as to the lamp or lamps which form the only parts that require replacement from time to time.
It is a further object of the invention to provide for an automatic switching-off of the irradiation apparatus upon expiry of a settable period of time and to avoid both, excessive and insufficient irradiation periods.
The above and further objects are met by an apparatus for treating dental objects with radiation of a selected spectral range as defined in the appending patent claims.